Mars Pathfinder was an ambitious mission to send a lander and a separate, remote-controlled rover to the surface of Mars, the second of NASA's Discovery missions.

Launched one month after Mars Global Surveyor, Pathfinder was sent on a slightly shorter seven-month trajectory designed for earlier arrival. The main spacecraft included a 10.6-kilogram, six-wheeled rover known as Sojourner capable of traveling 500 meters from the main ship at top speeds of 1 centimeter per second. The mission's primary goal was not only to demonstrate innovative, low-cost technologies, but also to return geological, soil, magnetic property, and atmospheric data.

After a seven-month traverse and four trajectory corrections (on 10 January, 3 February, 6 May, and 25 June 1997), Pathfinder arrived at Mars on 4 July 1997. The spacecraft entered the atmosphere and was then slowed by aerobraking, retrorockets, and a parachute before bouncing on the surface using cushioned landing bags that had deployed 8 seconds before impact.

Pathfinder landed at 16:56:55 UT on 4 July 1997 at 19.30° north latitude and 33.52° west longitude in Ares Vallis, about 19 kilometers southwest of the original target. Impact speed was about 10.5 meters per second; the spacecraft bounced several times before coming to a complete stop.

The next day, Pathfinder deployed the Sojourner rover on the Martian surface via landing ramps. Sojourner was the first wheeled vehicle to be used on any other planet of the solar system.

During its eighty-three-day mission, the rover covered hundreds of square meters, returned 550 photographs, and performed chemical analyses at sixteen different locations near the lander. The latter, meanwhile, transmitted more than 16,500 images and 8.5 million measurements of atmospheric pressure, temperature, and windspeed.

Data from the rover suggested that rocks at the landing site resembled terrestrial volcanic types with high silicon content, specifically a rock type known as andesite.

Although the planned lifetimes of Pathfinder and Sojourner were expected to be one month and one week, respectively, these times were exceeded by three and twelve times, respectively. Final contact with Pathfinder was at 10:23 UT on 27 September 1997. Although mission planners tried to reestablish contact for the next five months, the highly successful mission was officially declared terminated on 10 March 1998. After landing, Mars Pathfinder was renamed the Sagan Memorial Station after the late astronomer Carl Sagan.

Key Dates

4 Dec 1996: Launch (06:58:07 UT)

4 Jul 1997: Mars Landing (16:56:55 UT)

5 Jul 1997 - 25 Sep 1997: Sojourner Rover Operations

27 Sep 1997: End of Mission (10:23 UT)

Status: Successful

Fast Facts

The rover was named in honor of Sojourner Truth (right), a 19th century abolitionist and champion of women's rights.

The name was suggested by Valerie Ambroise, 12, of Bridgeport, CT. Other suggestions included Sacagawea, Athena and Thumbelina.

Sojourner rover operated for 84 days - 12 times longer than its designed lifetime of seven days.

Among the mission firsts: Pathfinder was the first spacecraft to bounce on another planet and Sojourner was the first wheeled rover to explore another planet. Soviet Lunokhod rovers had previously explored Earth's Moon.

Pathfinder was the second in NASA's Discovery program of low-cost missions with highly-focused science objectives.